Can't find the keyboard shortcut in keymap preferences
Open the keymap in the preferences (Edit > Preferences > Keymap) and select Key-binding in the drop-down next to the search box. The shortcut can be found by searching for the W key-binding. The Shift + Spacebar shortcut for the toolbar popup is a separate one.



You're looking for Set Tool By Name. (*)



(*) Now that you know its name, you can also search for it directly. The approach above works for any shortcut though, in case you don't know the operator's label.